Control apparatus for an internal combustion engine

A control apparatus comprising:

• an internal combustion engine having a plurality of cylinders and a plurality of fuel injectors, the plurality of cylinders are grouped into a first cylinder group and a second cylinder group;
• a first exhaust passage that is connected to said internal combustion engine, with an exhaust gas of said first cylinder group flowing therethrough;
• a second exhaust passage that is connected to said internal combustion engine, with an exhaust gas of said second cylinder group flowing therethrough;
• a third exhaust passage that is formed by merging of said first exhaust passage and said second exhaust passage;
• a centrifugal supercharger that is equipped with a turbine arranged at a merging portion of said first exhaust passage and said second exhaust passage or in said third exhaust passage;
• an exhaust gas purification device that is arranged in said third exhaust passage at a location downstream of said turbine of said centrifugal supercharger, with a catalyst having an oxidation function being received therein;
• a bypass passage that branches from said first exhaust passage, and merges into said third exhaust passage at a location upstream of said exhaust gas purification device, while bypassing said turbine;
• a waste gate valve that switches opening and closing of said bypass passage;
• and
• an electronic control unit operatively connected to said waste gate valve and said plurality of fuel injectors, said electronic control unit configured to:
• carry out an imbalance processing by controlling the plurality of fuel injectors such that an air fuel ratio of a mixture to be combusted in a cylinder of either one of said first cylinder group and said second cylinder group is made richer than a stoichiometric air fuel ratio, and an air fuel ratio of a mixture to be combusted in a cylinder of the other of said first cylinder group and said second cylinder group is made leaner than the stoichiometric air fuel ratio;
• and
• control said waste gate valve so as to open said bypass passage when the imbalance processing is carried out by said electronic control unit,
• wherein when said electronic control unit cannot control said waste gate valve to open said bypass passage, said electronic control unit controls the plurality of fuel injectors such that an air fuel ratio of a mixture to be combusted in each of a part of the cylinders of said first cylinder group is made leaner than the stoichiometric air fuel ratio, and at the same time, an air fuel ratio of a mixture to be combusted in each of the remaining cylinders of said first cylinder group is made richer than the stoichiometric air fuel ratio, and
• said electronic control unit controls the plurality of fuel injectors such that an air fuel ratio of a mixture to be combusted in each of a part of the cylinders of said second cylinder group leaner than the stoichiometric air fuel ratio, and at the same time, an air fuel ratio of a mixture to be combusted in each of the remaining cylinders of said second cylinder group is made richer than the stoichiometric air fuel ratio.